System and Method of Satellite Communication

ABSTRACT

In particular embodiments, a system may include a spacecraft and optical ground terminals. The spacecraft includes at least an optical space terminal and a space switch unit. The space switch unit is configured to receive physical layer data frames from one optical space terminal, regenerate data-link layer data packets based on the physical layer data frames and route the regenerated data-link layer data packets to another optical space terminal. The optical ground terminals are configured to receive data-link layer data packets by one of the optical ground terminals, encode the received data-link layer data packets into physical layer data frames, transmit encoded physical layer data frames from one of the optical ground terminals to a respective optical space terminal through multiple forward channels at a data rate of 1 Tbps or above, the encoded physical layer data frames are decoded by the respective optical space terminal.

FIELD OF THE INVENTION

This disclosure relates to the field of satellite communication, andmore particularly to optical satellite communication.

BACKGROUND

To provide quality Internet service to unconnected residences around theglobe, the infrastructure required to make a high capacity practicalnecessitates major advancements in terrestrial, airborne, andspace-borne telecommunications technologies. It is estimated that atseveral terabits-per-second (Tbps) telecom capacity per spacecraft,Internet delivery via satellites may become cost-competitive with thelowest-cost wired or wireless connectivity technologies. To realize thistechnological advance in telecom, substantial improvements in thecapacity of today's satellite communications networks, whether ingeostationary orbit (GEO) or medium-earth-orbit (MEO), low-earth-orbit(LEO) may be required.

Satellite data communication systems transfer data from a transmitter(TX) of one station to a receiver (RX) of another station. The TX or RXcan be ground-based, airborne, or spaceborne. Furthermore, multipleground-based stations (TX or RX) can be in communication with one ormore air or space platforms (RX or TX). These ground/airborne/spacebornetelecommunication systems support uplink and downlink of large andever-increasing volumes of data (e.g., Internet data).

To address high capacity and high performance needs, the fiber opticsindustry developed coherent fiber optic transceiver technologies usingdigital signal processors (DSPs) for the next generation of high-ratecommunications. DSP-based coherent transceivers increase performance ofthe satellite system using optical preamplification and offer higherspectral efficiency and lower power consumption. Moreover, theintegrated photonics technology employed in coherent transceiversprovides a competitive cost-benefit value.

SUMMARY OF PARTICULAR EMBODIMENTS

Currently, wireless or satellite Internet is often used in rural,undeveloped, or other hard to serve areas where the wired Internet isnot readily available. As the Internet access grows rapidly, highaggregated user data rates may be required for large volumes of datacommunication. The satellite data communication system can providequality Internet service to remote residences around the globe at veryhigh data rates over longer distances and much more cost-effective thanwired or wireless communication. The infrastructure required to makesuch a high capacity practical may necessitate major advancements interrestrial, airborne, and space-borne telecommunications technologies.It is estimated that at several terabits-per-second (Tbps) telecomcapacity per spacecraft may support uplink and return channelcommunication of large and ever-increasing volumes of data (e.g.,Internet data). Current technologies for free-space optical/lasercommunications (lasercom) may allow multi-Tbps uplink capacity from aground station to a MEO or GEO satellite along with Tbps-scale downlinkcapacity via a few beams. However, the total single spatial- andlongitudinal-mode uplink laser power required to achieve multi-Tbpsgateway link capacity per satellite is a limiting factor. Also, due toatmospheric effects, lasercom uplink and downlink availability perstation may be limited (e.g., on the order of 50 to 60% for aboveaverage ground sites).

The embodiments described herein provide an apparatus, a system or amethod that is directed to high data rates (e.g., 1 Tbps or above)satellite optical/laser communication through air and/or vacuum.Specifically, recovery of lost data frames is improved by applying datacorrection at the data-link layer over multiple spatially separatedoptical beams corresponding to channels at the physical layer. Thesystem may comprise one or more optical ground terminals, a spacecraftcomprising one or more optical space terminals and a space switch andRadio Frequency (RF) channel former, and one or more forward or returnatmospheric channels. The optical space terminals may communicate withthe optical ground terminals bi-directionally through theatmosphere/vacuum space via the forward or return atmospheric channels.

Particular embodiments may provide optical communication withearth-orbiting satellites using Optical Feeder Links (OFLs) to supporthigh data rate optical satellite communication through air and/or space.The Optical Feeder Links are the connections between ground stations anda telecommunication satellite, which utilize laser and opticaltechnologies to send and receive data (e.g., Internet Traffic). OpticalFeeder Links offer terabit/second throughput, with unmatched low costper bit, secure and immune from jamming and interference. The opticalsatellite communication uses optical beams to transmit data through theatmosphere or the atmosphere and vacuum. The data may be communicatedbetween two ground terminals, a ground terminal and a space terminal,two space terminals, or any suitable configuration of terminals.Additionally, any of the space terminals or ground terminals in any ofthe configurations described herein may operate as transmitters,receivers, or transceivers.

The embodiments disclosed herein are only examples, and the scope ofthis disclosure is not limited to them. Particular embodiments mayinclude all, some, or none of the components, elements, features,functions, operations, or steps of the embodiments disclosed above.Embodiments are in particular disclosed in the attached claims directedto a method, an apparatus, a storage medium, a system and a computerprogram product, wherein any feature mentioned in one claim category,e.g., method, can be claimed in another claim category, e.g., system, aswell. The dependencies or references back in the attached claims arechosen for formal reasons only. However, any subject matter resultingfrom a deliberate reference back to any previous claims (in particularmultiple dependencies) can be claimed as well so that any combination ofclaims and the features thereof are disclosed and can be claimedregardless of the dependencies chosen in the attached claims. Thesubject-matter which can be claimed comprises not only the combinationsof features as set out in the attached claims but also any othercombination of features in the claims, wherein each feature mentioned inthe claims can be combined with any other feature or combination ofother features in the claims. Furthermore, any of the embodiments andfeatures described or depicted herein can be claimed in a separate claimand/or in any combination with any embodiment or feature described ordepicted herein or with any of the features of the attached claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A illustrates an example satellite communication system inaccordance with particular embodiments.

FIG. 1B illustrates an examples data transmission of a satellitecommunication system in accordance with particular embodiments.

FIG. 2 is a simplified illustration of the optical data transmissionthrough the atmosphere in accordance with particular embodiments.

FIG. 3A is a schematic illustration of a system for data transmissionbetween a TX and a RX in accordance with particular embodiments.

FIG. 3B is an example schematic illustration of the TX of the system inFIG. 3A in accordance with particular embodiments.

FIG. 3C is an example schematic illustration of the RX of the systemshown in FIG. 3A in accordance with particular embodiments.

FIG. 4 is a block diagram of an example optical ground terminal of asatellite communication system shown in FIG. 1 in accordance withparticular embodiments.

FIG. 5 is a block diagram of an example optical space terminal of asatellite communication system shown in FIG. 1 in accordance withparticular embodiments.

FIG. 6 is a block diagram of an example of bi-directional communicationof a satellite communication system shown in FIG. 1 in accordance withparticular embodiments.

FIG. 7A is a block diagram of an example communication among opticalspace terminals of a satellite communication system shown in FIG. 1 inaccordance with particular embodiments.

FIG. 7B is a block diagram of an example communication redirection of asatellite communication system shown in FIG. 1 in accordance withparticular embodiments.

FIG. 8 illustrates an example method of optical satellite communicationin accordance with particular embodiments.

FIG. 9 illustrates another example method of optical satellitecommunication in accordance with particular embodiments.

DESCRIPTION OF EXAMPLE EMBODIMENTS

Specific details of particular embodiments of representative opticaldata communication systems and methods thereof are described below. Theinventive technology is directed to communication links between groundstation(s) and airborne or spaceborne platforms at data-rates that havenot been possible before and with mass/power/size that is significantlylower than transceivers that use conventional technology.

Briefly described, the inventive technology uses multiple optical beamsto communicate data through the atmosphere or through the atmosphere andvacuum. The data may be communicated between two ground stations,between a ground station and an airborne platform, between two airborneor two spaceborne platforms, between an airborne platform and aspaceborne platform, or any suitable combination thereof. Additionally,any of the stations or platforms in any of the configurations describedherein may operate as transmitters, receivers, or transceivers. Theindividual optical beams (which may correspond to individual channels)can carry independent data to establish multiple independent links froma transmitter (TX) to a receiver (RX), therefore increasing thethroughput of the system. The individual optical beams can operate ondifferent wavelengths. The beams may be produced by optical sources suchas lasers or light emitting diodes. In at least some embodiments, theinventive technology uses advanced modulation formats and coherentdetection (e.g., dual-polarization quadrature-phase-shift keying(DP-QPSK), binary PSK (BPSK), or Quadrature Amplitude Modulation (QAM))in conjunction with multiple optical beams, which were previouslythought to be incompatible). In other embodiments, the inventivetechnology uses direct detection (e.g., intensity modulated directdetection). Any suitable modulation format or technique may be employed.

Some embodiments of the inventive technology use coherent opticalcommunication. In coherent optical communications systems, informationto be conveyed across a link is modulated onto the amplitude and phaseof a transmitted optical carrier signal as a sequence of symbols chosenfrom a fixed alphabet of amplitude and phase pairs according to the datato be conveyed. As information is now encoded in the phase of thereceived optical signal, it cannot be directly recovered, as in a directdetection scheme, by a photo-detector, which measures intensity. Torecover the phase of the received signal, there are several differenttypes of demodulator structures that can be used. These demodulators canbe variants on the method of mixing the received optical signal with alocal reference signal, which results in the intensity of the mixedsignal being a function of the difference between the received signalphase and the local reference. This can then be measured by aphoto-detector and processed to estimate the transmitted symbol andcorresponding transmitted data sequence.

The inventive technology uses multiple beams separated spatially by adistance D, where D»r_(o), where r_(o) is a radius of a beam of lightand is compatible with coherent communications. We use multipletransmitters that are spatially separated. In particular embodiments,each transmitter sends light that can be separated from the light sentby the other transmitters. In particular embodiments, this separabilityis implemented by having each transmitter use a distinct optical carrierfrequency, such that the spectrum used by each transmitter is generallydistinct and non-overlapping. Each transmitter can have adequate spatialseparation from the others, such that the fading process isstatistically independent on each transmitter.

In particular embodiments, each transmitter-to-receiver link canimplement an independent physical layer forward error correction (FEC)code and channel interleaver that are designed to target channelimpairments whose coherence time is much less than that of the frequencynon-selective fading. Under some scenarios, this may result in blocks ofcodewords that are not recoverable by the physical layer FEC when thesignal level drops below the receiver sensitivity threshold (due tochannel fading). To correct for these errors, data-link layer FEC isintroduced. The data-link layer FEC encoder operates across theindividual channels and may have support across multiple channelcoherence times. In the event that the physical layer FEC and data-linklayer FEC codes were unable to recover the transmitted information, atransport layer protocol, such as TCP, can utilize an ARQ scheme asnecessary to retransmit lost data frames.

Prior to sending the data through the atmosphere, one or more dataframes are encoded with a data-link layer FEC code. In particularembodiments, the data-link layer FEC code is an erasure code. Inparticular embodiments, the erasure code used can be a fountain code. Inparticular embodiments, each data-link layer FEC encoded data frame(referred to herein as “encoded data frame”) may then be sent to one ofmultiple channels (described in further detail below). Within a channel,the symbols of the encoded data frames are encoded with a physical layerFEC code that can be exploited at the receiver to correct for errors dueto a number of effects including channel fading. At the physical layer,the use of codeword interleaving at the transmitter and correspondingcodeword de-interleaving at the receiver will spread a burst of errorsacross multiple codewords for correction by the decoder. The interleavedcodewords of a particular channel are then modulated onto light of adesignated wavelength for that channel (which may be different for eachof the multiple channels) and then transmitted through free space. Atthe RX, the light is collected by the receive aperture or apertures. Thereceived signal may then pass through a demultiplexer to produce datafrom individual optical beams (e.g., from the individual channels). Thedata in each individual channel can then be demodulated, de-interleavedto reconstitute the codewords, and then decoded to reconstitute theencoded data frames. Finally, one or more reconstituted encoded dataframes are passed through the data-link layer FEC decoder to produce thereconstituted data frames. Therefore, at the RX, a particular data framecan be: (i) received fully (e.g., no errors in the data frame); (ii)recovered using the error correction for that channel; or (iii) benon-recoverable using the error correction for that channel (e.g., thedata frame includes too many errors rendering it unrecoverable). Insteadof declaring as lost the non-recoverable data frame and retransmittingit, the inventive technology applies additional data frame recoveryacross one or multiple channels to improve the overall frame recovery.For example, data-link layer FEC in the form of an erasure code (e.g., a“fountain code”) can be implemented over multiple data frames prior totransmitting data frames from the TX to the RX over individual channels.If the recovery within the channel fails, the data-link layer FECerasure code applied over multiple channels and data frames may be usedin many cases to recover the erased data frame without retransmittingthe data frame and without the concomitant increase in the latency ofdata transmission.

FIG. 1A illustrates an example satellite communication system inaccordance with particular embodiments. The satellite communicationsystem 100 may comprise one or more optical space terminals 102 a and102 b, one or more optical ground terminals 104 a and 104 b, and a spaceswitch and RF channel former 106. The communications between the opticalspace terminals 102 a and 102 b and the respective optical groundterminals 104 a and 104 b can be bi-directionally through one or moreatmosphere channels. The optical space terminals 102 a and 102 b canhave receivers (RXs) for receiving uplink data from the respectiveoptical ground terminals 104 a and 104 b, wherein the optical groundterminals 104 a and 104 b may have counterpart transmitters (TXs) fortransmitting the uplink data. In particular embodiments, TXs may residein the optical space terminals 102 a and 102 b while the counterpart RXsreside in the optical ground terminals 104 a and 104 b, wherein the TXsencode the data frames while the counterpart RXs decode the encoded dataframes. Vice versa, RXs may reside in the optical space terminals 102 aand 102 b while the counterpart TXs reside in the optical groundterminals 104 a and 104 b, wherein the RXs decode the data frames whilethe counterpart TXs encode the encoded data frames.

In particular embodiments, the optical ground terminals 104 a and 104 bmay comprise a physical layer 110 at the lowest level, and/or adata-link layer 120. Next level above the data-link layer 120 may be anetwork layer 130 including a network/traffic management interface 132and a fiber network interface 134.

The network layer 130 delivers data in the form of packets from a sourceto a destination of a system (e.g., satellite system). In general, thenetwork layer 130 may use a data-link layer and a physical layer todeliver the packets from the source to the destination. The data can bereceived at the network layer 130, wherein the network layer 130 can bea high rate network layer (e.g., 100 GbE or above) of the satellitecommunication system. The received data may be connected to the fiberoptic networks through the fiber network interface 134. The fibernetwork interface 134 can be integrated into the computation devices, orother components in the fiber optic networks. For example, a 10+ Gbfiber network interface can be used in a 100 GbE network of thesatellite communication system. The fiber network interface 134 can be agateway allowing computation devices to be connected to various types offiber optic networks.

The network traffic management interface 132 can filter and route thenetwork traffic to an optimum resource for significantly increasingnetwork performance. In particular embodiments, the network trafficmanagement interface 132 can assign user beam labels to the receivedprotocol packets (e.g., IP packets) and route the labeled IP packets tothe next layer (e.g., the data-link layer 120).

At the data-link layer 120, the bits of the received data packets arearranged into data frames for delivering to the satellite system. Thedata frames are encoded by the data-link layer erasure encoder and sentas bit streams through the physical layer 110. The physical layer 110contains functionality necessary to carry the stream of data bits to theoptical space terminals 102 a and 102 b through a medium. The physicallayer 110 may comprise an optical beam control 122, optical poweramplifiers (PA) 124, optical low noise amplifiers (LNA) 126, opticalmodem & channel encode/decode components 128. The encoded data framesmay be distributed to one of the multiple data channels in the physicallayer 110 by a distributor. In each of the multiple data channels, theencoded data frames may be encoded again by a physical layer FEC channelencoder into codewords, and the codewords may be converted to theoptical signals by the optical modem. In the physical layer 110, theelectrical signals may be converted to the optical signals by theoptical modems, where the electrical signals may be embedded withoptical or laser beams. The optical beams, such as laser light carryingthe electrical signals, may be modulated by a modulator and amplified byone of the optical LNAs 126 and/or one of the optical PAs 124, whereinthe optical PAs 124 may have a power of 100 watts (W). The amplifiedoptical beams may be emitted through the medium by the optical beamcontrol 122. The optical beam control 122 may ensure that the laserbeams are pointed to a respective spacecraft or the optical spaceterminal. Especially, since the spacecraft or the optical spaceterminals 102 a and 102 b may be moving objects, the optical beamcontrol 122 may track the position of the moving objects and configurethe optical ground terminals 104 a and 104 b to follow the moving objectprecisely.

In particular embodiments, the optical space terminals 102 a and 102 bmay comprise a physical layer including an optical beam control 112, anoptical power amplifier (PA) 114, an optical low noise amplifier (LNA)116, optical modem & channel encode/decode components 118 including anoptical modem and a channel decoder or encoder. In the physical layer,the optical beam control 112 may ensure that a respective optical groundterminal points and follows the optical space terminal precisely forreceiving the optical beams. The optical beams may be received by theoptical beam control 112 and be amplified by the optical PA 114 and/oroptical LNA 116. The amplified optical beams may be demodulated by ademodulator and converted to the electrical signals by the opticalmodem.

During the forward channel communication, the optical ground terminal104 a may emit optical beams carrying encoded data to the optical spaceterminal 102 a through multiple uplink atmosphere channels 140 i (e.g.,four uplink channels), wherein the received optical signals may bedecoded and converted from the optical signals to the electricalsignals. During the return channel communication, the optical spaceterminal 102 a may emit optical beams carrying encoded data to theoptical ground terminal 104 a through a downlink atmosphere channel 150,wherein the received optical signals may be decoded and converted fromthe optical signals to the electrical signals. Each of the opticalground terminals 104 a and 104 b may be coupled with a respectiveoptical space terminal. While a forward channel communication may beconducted by one pair of the optical ground terminal (e.g., opticalground terminal 104 a) and optical space terminal (e.g., optical groundterminal 102 a), a return channel communication may be conducted by adifferent pair of optical ground terminal (e.g., optical ground terminal104 b) and optical space terminal (e.g., optical ground terminal 102 b)concurrently. In particular embodiments, the return channelcommunication may have multiple return atmosphere channels.

Additionally, a transport layer above the network layer 130 may betasked with process-to-process delivery. For example, a process mayrequire multiple data packets to transfer a complete email message witha suitable order of the packets, confirmation of the error-free statusof the packets, etc. The next level of abstraction above the transportlayer is an application layer that specifies the shared protocols andinterface methods used by the hosts in a communications network. Thetransport layer and the application layer are not shown in FIG. 1.

In particular embodiments, the space switch and RF channel former 106including a space switch 160 may control the operation of the opticalspace terminals 102 a and 102 b, such as the communications between theoptical space terminals 102 a and 102 b and the respective opticalground terminals 104 a and 104 b, or the communications between theoptical space terminals 102 a and 102 b. Further, the space switch 160may function as a make-before-break (MBB) switch which may detectupcoming communication troubles and redirect communication from one ofthe optical space terminals to another one of the optical spaceterminals to avoid communication interruption. For example, in the eventthat the communication between an optical space terminal 102 a and anoptical ground terminal 104 a encounters problem (e.g., bad weather),the space switch 160 can redirect the communicate from the optical spaceterminal 102 a to another optical space terminal 102 b which isavailable at current moment. Therefore, the communication can becontinued between the optical space terminal 102 b and the opticalground terminal 104 a to prevent the interruption. In particularembodiments, the upcoming communication troubles may be detected by theoptical space terminals 102 a and 102 b, the optical ground terminals104 a and 104 b, or any other components in the satellite communicationsystem.

In particular embodiments, the satellite communication system can buildan optical communication channel, which enables the satellitecommunication system to fully regenerate user information packets on aspacecraft and route the user's information packets among the opticalspace terminals. The spacecraft mounted with the one or more opticalspace terminals can function as a data center on which the user'sinformation data packets can be routed from one destination to anotherdestination, such as from San Diego to Menlo Park, wherein eachdestination may be associated with a corresponding optical spaceterminal. The space switch and RF channel former 106 may include aregenerative multi-channel RF modem 162, which may compriseencoder/decoder and modulator/demodulator. The multi-channel RF modem162 may comprise 100-1000 channels, each channel may have a symbol rateof 50-1000 Msym (symbol) per second and a power of 2-4 W. Above thespace switch and RF channel former 106, the spacecraft may include anup/down converter 164 for controlling the uplink and return channelcommunication and PA/LNA combinations 166, wherein each of the multiplechannels may have a corresponding PA/LAN combination for filtering thenoise and enhancing the signals.

FIG. 1B illustrates an examples data transmission of a satellitecommunication system in accordance with particular embodiments. The datatransmission may involve multiple layers including the physical layer110, the data-link layer 120, and the network layer 130 of FIG. 1A. Dataframes of the uplink or downlink data can be formed at a transmittingdata-link layer 120 a to include data bits and frame header/footer. Thedata frames 125 a may be transferred to a transmitting physical layer110 a, where the data frames 125 a can be modulated and sent through atransmission medium 105 (e.g., the atmosphere or optical fiber). Thisstream of data bits can be reformatted as a new data frame 125 b at areceiving data-link layer 120 b through a receiving physical layer 110 bin the optical space terminals 102 a and 102 b. In some instances, theheader/footer data may be removed, and the new data frame 125 b is nextpassed to the network layer for further routing.

FIG. 2 is a simplified illustration of the optical data transmissionthrough the atmosphere in accordance with particular embodiments. Forexample, the optical data transmission through the atmosphere may occurbetween the optical space terminal 102 a and the optical ground terminal104 a through multiple uplink atmosphere channels 140 i of FIG. 1A. A TX210 may reside in the optical ground terminal 104 a and a counterpart RXmay reside in the optical space terminal 102 a, or vice versa.

A multi-channel system 20 can have the TX 210 that includes multipleapertures 212 i for transmitting data streams that are encoded in laserbeams 214 i. The laser beams 214 i can operate at different wavelengthsAi. As illustrated in the example of FIG. 2, each beam 214 i may carrylight at a single wavelength corresponding to a single data stream orchannel. In other embodiments, each beam 214 i may carry light atmultiple wavelengths corresponding to multiple data streams or channels.Although the specific example of laser beams is provided, it iscontemplated that in particular embodiments, optical sources other thanlasers can be used including, for example, light emitting diodes. Theseparation between any two adjacent beams 214 i is denoted as D. In atleast some embodiments of the inventive technology, the laser beams 214i transmit independent data streams through the air or vacuum, thereforeincreasing throughput of the system 20. The laser beams 214 i arereceived by one or more RX's 220 that include receiving apertures andsuitable optics to allow demodulators to coherently demodulate themodulated optical signal into a sequence of numerical values thatestimate the transmitted symbol or a set of likelihood ratios for eachpossible symbol realization. In particular embodiments, one of the TX210 and RX 220 can reside at a ground station, while its RX/TXcounterpart is airborne or spaceborne.

In other embodiments, both the TX and RX can be ground-based orairborne/spaceborne. In at least some embodiments, turbulence 230 causesuneven densities of air along the path of the laser beam. These unevendensities of air in turn change the refractive index along the path ofthe individual laser beams 214 i. Propagation through the variablerefractive index along the beams' path results in different intensitiesof the laser beams 214 i arriving at the RX 220. Therefore, the datastreams of the laser beams 214 i experience signal fading to differingdegrees. In at least some embodiments, the separation between the beamsD is large enough that the fading process is not correlated betweenbeams 214 i. Depending on sensitivity of the RX 220, signal intensity insome laser beams 214 i may fall below the sensitivity level of the RX,thus causing errors in the data stream. As explained above, moderatesignal fading and/or other data errors in the channel may be correctedusing the physical layer FEC code and channel interleaving. The physicallayer FEC scheme can be based, for example, on low-density parity-checkcodes (LDPC), turbo product codes, or braided or concatenated algebraiccodes such as BCH or Reed Solomon. However, in many practicalapplications the physical layer FEC code cannot correct for severechannel-fading-induced errors. In particular embodiments, when thephysical layer error correction within the channel cannot fully recoverthe lost data frames, an additional error correction across the channelsperformed at the data-link layer 120 is used to avoid retransmission ofthe data frames. The error correction at the data-link layer isexplained with reference to FIG. 3A below.

FIG. 3A is a schematic illustration of a system for data transmissionbetween a TX 30A and a RX 30B in accordance with particular embodiments.In particular embodiments, each of the TX 30A and/or RX 30B can be onthe ground, airborne or spaceborne. Multiple laser beams of themulti-channel system 20 can transfer independent data streams betweenthe TX 30A and RX 30B to increase the throughput of the datatransmission. Details of the TX 30A and RX 30B and the functionalitiesthereof are discussed in the following sections.

FIG. 3B is an example schematic illustration of the TX of the system inFIG. 3A in accordance with particular embodiments. FIG. 3C is an exampleschematic illustration of the RX of the system shown in FIG. 3A inaccordance with particular embodiments. FIG. 3B illustrates the TX 30Athat processes K data frames 310. The incoming data frames 310 can beencoded using a data-link layer FEC encoder 315. For example, thedata-link layer FEC code can be applied to a sequence of K data frames310 to produce a sequence of N encoded data frames 320. In particularembodiments, the first K encoded data frames 320 can be identical to theoriginal K data frames 310 to reduce average latency of the datatransfer, while the subsequent N-K encoded data frames 320 are used asrepair frames. In particular embodiments of the present technology, thedata-link layer FEC encoder 315 is an erasure code encoder that usesfountain codes to generate N encoded data frames 320 from the K dataframes 310. As explained below with reference to FIG. 3C, a RX can usethe fountain code to decode the received encoded data frames and torecover the missing data frames that were not recoverable using physicallayer FEC decoding. Therefore, the encoded data frames 320 can be usedto recover the lost data frames at the data-link layer, therebyobviating the need to retransmit the lost data frames over the highernetwork layers having higher data latency.

In particular embodiments, each of the N encoded data frames 320 arepassed through a distributor 325 and are routed to one of multiple datachannels 314 i. In particular embodiments, the system 30A includes Gmultiple data channels 314 i in parallel. A sequence of N encoded dataframes 320 can be distributed across multiple independent data channels314 i, with a subset of the encoded data frames 320 being sent over eachindependent data channel 314 i. In particular embodiments, thedistributor 325 distributes encoded data frames to data channels in around-robin fashion. In particular embodiments, the encoded data frames320 are further encoded using physical layer FEC encoders 330 in eachdata channel to encode the encoded frames 320 into codewords 331 i. Ineach data channel, the physical layer FEC encoder 330 encodes additionalerror-correction bits to the encoded data frames 320, allowing for thecorrection of some channel errors at the receiver after the codewordsare received in the corresponding data channel of the RX. After thephysical layer FEC encoder 330, the symbols of the codewords 331 i canbe interleaved by channel interleavers 335 into interleaved codewords336 i. In particular embodiments, for each data channel, a modulator 340modulates the laser light of a designated wavelength according tosymbols/bits of the interleaved codewords 336 i. As explained above, theinterleaved and modulated codewords can be transmitted from the TX 30Ato the RX 30B through independent transmission medium channels (e.g.,using multiple laser beams 214 i across air or space) in parallel toincrease throughput of the data transmission. Each of the plurality ofspatially separated beams 214 i may carry data from one or more of thedata channels.

In FIG. 3C, the interleaved and modulated codewords can be receivedthrough single or multiple apertures 350 and de-multiplexed intoindividual data channels that each correspond to a particularwavelength. Within each data channel, demodulator 355 can demodulate thereceived data into interleaved codewords 356 i. In particularembodiments, in each data channel, the deinterleaver 360 restores thesequence of symbols of the individual interleaved codewords 356 i totheir pre-interleaved ordering in 361 i. Next, physical layer FECdecoder 365 operates on the codewords 361 i of the data channel tocorrect the bit/symbol errors in the codewords 361 i of the particulardata channel. This may occur in each of the G data channels in parallel.In this step, the encoded data frames are reconstituted from thephysical layer FEC decoded symbols/information bits. If the number oferrors in a particular codeword 361 i is below the threshold that thephysical layer FEC decoder 365 is designed to correct, the originalencoded frames 320 contained within or portions encompassed by thecodeword are reconstructed and exported as encoded data frames 375.However, if the number of errors in a codeword 361 i exceeds thecorrection capability of the physical layer FEC decoder 365, thatcodeword is declared un-decodable and all encoded data frames containedwithin the codeword or that have portions encompassed by the codewordmay have uncorrectable errors which upon detection will result in thatencoded data frame being declared as erased. In general, depending onthe number of the correction bits available to the physical layer FECdecoders 365, not all channel errors will be correctable, resulting inat least some lost encoded data frames.

To recover the erased encoded data frames that are un-decodable with thephysical layer FEC decoders 365, an additional data frame recovery canbe executed over multiple encoded data frames 375 using data-link layerFEC decoder 380, which, for example, may use erasure codes such asfountain codes. If successful, this data frame recovery at the data-linklayer reconstructs the original data frames 310 without the generallyundesirable requirement of retransmission of the data frames throughhigher layers (e.g., at the transport layer). In particular embodiments,prior to being received by the data-link layer FEC decoder 380, thesequence of encoded data frames can be sent through a selector 370 as Lencoded data frames. The selector 370 may operate at the frame rate ofthe receiver. In particular embodiments, the selector 370 may performbuffering and/or reordering of the encoded data frames 375 prior tosending them, one frame at a time, to the data-link layer FEC decoder380. The data-link layer FEC decoder 380 produces output frames 390,which may or may not be the same as original data frames 310. Thedata-link layer FEC decoder 380 will succeed at recovering all of theoriginal frames 310 (i.e., output frames 390 will be the same asoriginal frames 310) provided that L is greater than or equal to K+Owhere 0, called the overhead, is a property of the data-link layer FEC.The code parameters, N, K, 0, and the size of the data frame are chosento meet a desired performance level, typically a bit error or a packetloss rate, while trading off the throughput and latency.

FIG. 4 is a block diagram of an example optical ground terminal of asatellite communication system shown in FIG. 1 in accordance withparticular embodiments. The optical ground terminal 400 may comprise aphysical layer 410 at the lowest level, and/or a data-link layer 420,and/or a network layer 430. The level above the data-link layer 420 maybe a network layer 430 including a network/traffic management interface432 and a fiber network interface 434.

As described above, the network layer 430 delivers data in the form ofpackets from a source to a destination of a receiving system (e.g.,satellite system). The data can be received at the network layer 430,and the received data may be connected to the fiber optic networksthrough the fiber network interface 434. The fiber network interface 434can be a gateway allowing computation devices to be connected to varioustypes of fiber optic networks.

In particular embodiments, the network traffic management interface 432can filter and route the network traffic to an optimum resource forsignificantly increasing network performance. The network trafficmanagement interface 432 can assign user beam labels to the receivedprotocol packets (e.g., IP packets) and route the labeled IP packets tothe next layer (e.g., the data-link layer 420). For example, a firstgroup of IP packets is labeled with user beam one, a second group of IPpackets is labeled with user beam two, a third group of IP packets islabeled with user beam three, a fourth group of IP packets is labeledwith user beam four, etc. The network traffic management interface 432may monitor the network traffic and effectively route the labeled groupsof IP packets to the data-link layer 420, to reduce network congestion,latency, or packet loss for efficient use of network bandwidth in thehigh-speed satellite communication system. The network layer 430 usesthe network address of the packet, e.g., IP address, to deliver thepacket to the receiving system.

At the data-link layer 420, the bits of the received data packets arearranged into data frames for delivering to the receiving system. Thedata frames may include suitable headers and/or footers (e.g.,source/destination addresses, error detection information, flow controlinstructions, etc.). The data frames are encoded by the data-link layererasure encoder 315 and sent as bit streams through the physical layer410, wherein the data-link layer FEC encoder 315 may be an erasure codeencoder. The data-link layer FEC encoder or packet erasureencoder/decoder 315 of FIG. 3B can conduct data-link layer erasureencoding during transmitting and data-link layer erasure decoding duringreceiving procedure. As described above, the data frames encoded withthe erasure code encoder can recover the missing data frames which areunrecoverable using physical layer FEC decoding, thereby obviating theneed to retransmit the lost data frames over the higher network layershaving higher data latency.

The physical layer 410 contains functionality necessary to carry thestream of data bits to the optical space terminals 102 a through amedium. The physical layer 410 may comprise an optical beam control 422,optical PAs 424, optical LNAs 426, and optical modem & channelencode/decode components 428. The encoded data frames may be distributedto one of the multiple data channels (e.g., four channels) in thephysical layer 410 by a distributor. In each of the multiple datachannels, the encoded data frames may be encoded again by a physicallayer FEC channel encoder/decoder 414 i into codewords, and thecodewords may be sent to a modulator through respective individualinterleaver channel (e.g., one of the four channels), and be convertedto the optical beams by an optical modem 412 i.

The optical modem & channel encode/decode components 428 may comprisethe optical modem 412 i and FEC channel encoder/decoders 414 i formultiple data channels 314 i of FIG. 3B, wherein each of the multipledata channels 314 i has a respective FEC channel encoder/decoder 414 i.The optical modem 412 i can provides electrical to optical conversion ofelectronic communication and data signals for transmission using highspeed fiber optic cable. The optical modem 412 i can simultaneouslyreceive incoming optical signals and convert them to the originalelectronic signal allowing for full duplex transmission. The opticalmodem 412 i can have single channel or multi-channel configurations andcan be mounted on the optical terminals including on the ground or inspace.

The optical beams, such as laser light carrying the electrical signals,may be modulated by a modulator 340 and amplified by one of the opticalLNAs 426 i and/or one of the optical PAs 424 i, and can be transmittedto the optimal space terminals 102 through multiple uplink atmospherechannels 140 i. The modulator 340 may modulate the laser light of adesignated wavelength according to the interleaved codewords 336 i. Themodulated laser light then can be processed with the optical PAs 424 i.The optical PA 424 i and optical LNA 426 i can improve intensity oflaser beam carrying encoded/decoded data by eliminating the noise andenhancing the encoded/decoded data. The optical PA is a device thatamplifies an optical signal directly, without the need to first convertit to an electrical signal. The optical PA is commonly used forenergizing the modulated laser light and to produce high power lasersystems. Each of the multiple data channels 314 i may have its ownoptical PA. The optical PAs 424 i are important components in thesatellite communication system for transmitting/receiving data in longdistance telecommunication links, such as throughout theatmosphere/vacuum. The optical LNA 426 i can amplify a very low-powersignal (e.g., the encoded data frames) without significantly degradingits signal-to-noise ratio, which can be designed to minimize additionalnoise. For example, a typical LNA may supply a power gain of 100 (20decibels (dB)) while decreasing the signal-to-noise ratio by less than afactor of two (a 3 dB noise figure (NF)). This amplification can ensurethe encoded data frames are sufficiently strong for transmitting,resulting in minimized data loss in the future process. There areseveral different physical mechanisms that can be used to amplify thelaser light, which correspond to the major types of optical poweramplifiers including doped fiber amplifiers, semiconductor opticalamplifiers (SOAs), Raman amplifiers, or parametric amplifiers. Theoptical beams used for communication can be aligned with a communicationterminal located on an earth-orbiting satellite (e.g., the optical spaceterminals 102 a and 102 b) and a terminal located on a ground station(e.g., the optical ground terminals 104 a and 104 b). A beam acquisitioncomponent of the optical ground terminal 104 a may comprise a group ofsubassemblies and pointing and tracking control.

The amplified optical beams may be emitted through the medium by theoptical beam control 422 i. The optical beam control 422 i may ensurethat the laser beams are pointed to a respective spacecraft or theoptical space terminal. In particular embodiments, the optical beamcontrol 422 i is used to control the multiple apertures 212 i for aimingthe laser beams 214 i to the optical space terminals 102. The opticalbeam control can conduct acquisition, pointing and tracking of lasersignals (e.g., the laser beams 214 i). The optical beam control 422 ican have a function to get the light beams efficiently coupled with theoptical beams, which is a challenging task because of possible holes inthe light beams. Another important task for the optical beam control 422i can be accurately directing the optical beams to the destinations,such as the optical space terminals 102 a and 102 b or a spacecraft, ina timely manner. Especially, since the spacecraft or the optical spaceterminals 102 a and 102 b may be moving objects, the optical beamcontrol 422 i may track the position of the moving objects and configurethe optical ground terminals 104 a and 104 b to follow the moving objectprecisely.

FIG. 5 is a block diagram of an example optical space terminal of asatellite communication system shown in FIG. 1 in accordance withparticular embodiments. The optical space terminal 500 may comprise aphysical layer including an optical beam control 502, an optical poweramplifier (PA) 504, an optical low noise amplifier (LNA) 506, an opticalmodem & channel Encode/Decode 508. During the forward channelcommunication, the optimal space terminal 500 may receive optical beamsthrough the multiple uplink atmosphere channels 140 i of FIG. 1 anddecode the received optical beams. During the return channelcommunication, the optimal space terminal 500 may encode the data framesand transmit the optical beams to the optical ground terminal 104 athrough the return channel 150 of FIG. 1. The optical PA 504 and opticalLNA 506 can improve intensity of laser beam carrying encoded/decodeddata by eliminating the noise and enhancing the encoded/decoded data.The optical beam control 502 may ensure that the laser beams aredirected to a respective spacecraft or the optical space terminal.

In particular embodiments, the optical beam control 502 is used tocontrol the multiple apertures for receiving the laser beams from theoptical ground terminal 104 a, similarly to the optical beam control 422i described above.

In particular embodiments, the received optical beams then can beamplified by the optical PAs 504 and/or optical LNA 506, similarly tothe optical PAs 424 i and/or optical LNA 426 i as described above. Thereceived amplified optical beams can be processed by the demux 350,demodulators 355, channel deinterleavers 360, and the physical layer FECdecoders 365 of FIG. 3C.

As described above, the optical modem and channel encoder/decoder 508can provides optical to electrical conversion of electroniccommunication and data signals for reception using high speed fiberoptic cable. The optical modem 510 can have single channel ormulti-channel configurations and can be mounted on the opticalterminals, on the ground or in space. For example, the optical modem 510mounted on the optical space terminal 500 may have a configuration ofthe single channel 150. The channel encoder/decoder 512 can conductphysical layer decoding during receiving forward channel communication.The optical modem 510 and channel encoder/decoder 512 can be implementedwith programmable logic (e.g., FPGA) or integrated circuit (IC)technologies.

FIG. 6 is a block diagram of an example of bi-directional communicationof a satellite communication system shown in FIG. 1 in accordance withparticular embodiments. The optical space terminals 102 a and 102 b andthe optical ground terminals 104 a and 104 b of FIG. 1 may performbi-directional communication including uplink and down linkcommunications. The forward channel communication of the satellitecommunication system refers to transmission of signals from an earthstation (e.g., the optical ground terminal 104 a) to a space system(e.g., the optical space terminal 102 a), or any high-altitude platformstation. The return channel communication can be a reversed forwardchannel communication. The return channel communication refers to thetransmission of signals from a space system (e.g., the optical spaceterminal 102 b or any high-altitude platform station) to an earthstation (e.g., the optical ground terminal 104 b).

In particular embodiments, the satellite communication system canperform both the forward channel communication and the return channelcommunication through the atmosphere or vacuum using fiber opticaltechnique. The forward channel communication can include encoding theuplink data and converting electrical signals of the uplink data intooptical signals by the optical ground terminal 104 a, transmitting theuplink data carried on the optical beams from the optical groundterminal 104 a to the optical space terminal 102 a through multiple freespace fading atmospheric channels 610 (e.g., four channels), andconverting the received optical beams into the electrical signals of theuplink data and decoding the received uplink data by the optical spaceterminal 102 a. Details of the forward channel communication isdescribed previously.

In particular embodiments, the satellite communication system canperform the down forward channel communication which includes encodingthe downlink data and converting electrical signals of the downlink datainto optical signals by the optical space terminal 102 b, transmittingthe downlink data carried on the optical beams from the optical spaceterminal 102 b to the optical ground terminal 104 b through a singlefree space fading atmospheric channel 620, and converting the receivedoptical beams into the electrical signals of the downlink data anddecoding the received downlink data by the optical ground terminal 104b.

As shown in FIG. 6, the return channel communication can occur betweenthe optical space terminal 102 b and the optical ground terminal 104 bwhile the forward channel communication can occur between the opticalspace terminal 102 a and the optical ground terminal 104 a. Theone-to-one pairing between the optical space terminals and the opticalground terminals can be configured by the satellite system and can beupdated dynamically with the real-time communication situation, such ascommunication interruption or availability of the terminals.

FIG. 7A is a block diagram of an example communication among opticalspace terminals of a satellite communication system shown in FIG. 1 inaccordance with particular embodiments. The satellite communicationsystem may have one or more optical space terminals including an opticalspace terminal 702 a and another optical space terminal 702 b, a spaceswitch 710, and a RF channel former 720, wherein the optical spaceterminal 702 a and 702 b can receive or transmit physical layer leveldata. The RF channel former 720, along with other components in thespace switch and FR channel former unit, may be used to process thephysical layer data into the data-link layer or higher layer datapackets. The details of the data routing operation are describedpreviously.

In particular embodiments, the satellite communication system can buildan optical communication channel, which enables the satellitecommunication system to fully regenerate user information packets on aspacecraft and route the user's information packets among the opticalspace terminals. The spacecraft mounted with the one or more opticalspace terminals can function as a data center on which the data packetsat data-link layer or higher can be routed from one destination toanother destination. For example, the physical layer level data receivedby the optical space terminal 702 a can be forwarded to the space switchand RF channel former unit, and the physical layer level data may beregenerated into the data-link layer level data packets on thespacecraft. The regenerated data-link layer level data packets may bererouted to the optical space terminal 702 b. If the optical spaceterminal 702 a is associated with a ground terminal at a destination(e.g., San Diego), and the optical space terminal 702 b is associatedwith another ground terminal at another destination (e.g., Menlo Park),the satellite system may be operated as a data center rerouting the datapackets from San Diego to Menlo Park.

FIG. 7B is a block diagram of an example communication redirection of asatellite communication system shown in FIG. 1 in accordance withparticular embodiments. In particular embodiments, the space switch 710can be a make-before-break (MBB) switch and can redirect the trafficaround at packets to packets level, wherein the packets may be thepackets at the data-link level or higher. For example, the space switch710 can be a Multiprotocol Label Switching (MPLS) directing data packetsfrom one network terminal (e.g., the optical space terminal 702 a) tothe next network terminal (e.g., the optical space terminal 702 b) basedon short path labels for high-performance telecommunications networks,such as the satellite communication system. While one of the opticalspace terminals is a main operating space terminal 702 a, one or morealternative optical space terminals may be included in the system asbackups, such as the alternative optical space terminal 702 b. When theoperating optical space terminal 702 a encounters potentialcommunication problems, the alternative optical space terminal 702 b maybe located for taking over the ongoing uplink or return channelcommunication from the operating optical space terminal 702 a. The spaceswitch 710 (e.g., a terabit switch) may redirect the ongoingcommunication to the alternative optical space terminal 702 b to preventa possible communication breakdown. The satellite system may determinewhich optical space terminal is suitable for picking up the ongoingcommunication and redirect the communication thereto. For example, thesatellite system may be able to determine the optical ground terminal702 b is available and has the appropriate capacity to take over theongoing communication, and the ongoing communication can be redirectedfrom the optical ground terminal 702 a to the optical ground terminal702 b.

For example, the optical space terminal 702 a is performing a forwardchannel communication with a respective optical ground terminal 706 a.The optical space terminal 702 a can be paired with the optical groundterminal 706 a, such that the apertures in the optical ground terminal706 a can be adjusted for accurately aiming and emitting optical beamsto the optical space terminal 702 a. If a possible communication problemis detected by the satellite system, such as possible power outage orpoor reception due to bad weather, the satellite system may determinethat the optical space terminal 702 b is available and can be the idealcandidate for picking up the ongoing forward channel communication fromthe optical space terminal 702 a.

In particular embodiments, the space switch 710 may command therespective optical ground terminal 706 a to adjust its apertures fromaiming the optical space terminal 702 a to aiming the optical spaceterminal 702 b. In the meanwhile, the optical space terminal 702 b mayadjust its apertures for aiming the optical ground terminal 706 a to getready for forward channel communication thereto. Before the adjustmentof the apertures are completed or the optical space terminal 702 b isready for receiving new uplink data from the optical ground terminal 706a, the optical space terminal 702 a may continue receiving the uplinkdata from the optical ground terminal 706 a and forward the receiveduplink data to the optical space terminal 702 b for a smoothcommunication transition. In particular embodiments, the optical groundterminal 706 a may transmit the uplink data to both the optical spaceterminal 702 a and the optical space terminal 702 b while the aperturesare adjusted for establishing the new communication link. The spaceswitch 710 can synchronize the adjustments of terminal apertures andredirection of uplink data communication, such that the communicationtransition from the optical space terminal 702 a to optical spaceterminal 702 b can be smooth and without interruption. Alternately, inparticular embodiments, the optical ground terminal 706 a can buffer thelast portion of the uplink data and resend it to the optical spaceterminal 702 b when the optical space terminal 702 b is ready, forpreventing a communication interruption and possible data transmissionerrors.

Similarly, a return channel communication can be redirected followingthe same principle. In particular embodiments, one or more redirectingmechanism discussed above can be utilized by the satellite system for asmooth transition to prevent communication breakdown.

FIG. 8 illustrates an example method of optical satellite communicationin accordance with particular embodiments.

In particular embodiments, a bi-directional data transmission of asatellite communication may comprise a forward channel communication anda return channel communication, wherein the forward channelcommunication 800 may start at step 810, data-link layer data packetsare received by a TX of an optical ground terminal, wherein the receiveddata-link layer data packets are encoded by a data-link layer packeterasure forward error correction (FEC) encoder. The received data-linklayer data packets are first arranged into a plurality of data frames,and the plurality of data frame are encoded by the data-link layerpacket erasure FEC encoder. The number of the data frames beforeencoding may be different than the number of the encoded data frames.The encoded data frames then are sent to the physical layer.

At step 820, the encoded data frames are received from the data-linklayer. The received encoded data frames are processed at the physicallayer. The encoded data frames are distributed by a distributor to oneof a plurality of data channels. Within each of the data channels, theencoded data frames are encoded again by a physical layer FEC encoderinto codewords. Then the codewords are interleaved by a channelinterleaver.

At step 830, the interleaved encoded data frames are inputs to anoptical modem which perform the conversion between the electricalsignals and optical signals. The outputs of the optical modem are theoptical signals, wherein the optical signals are modulated by amodulator. After being modulated, the optical signals are amplified byan optical power amplifier (PA) and/or an optical low-noise amplifier(LNA). The modulated and amplified optical signals are coupled withlaser beams by a beam control, wherein the beam control also ensure thatthe transmitting apertures of the optical ground terminal are aimed tothe receiving apertures of a respective optical space terminal.

At step 840, the laser beams are transmitted through the air or vacuumvia multiple forward channels. Each laser beam may carry light at aspecific wavelength corresponding to one of the data channels. Thus,multiple laser beams may transmit independent data streams through theair or vacuum for increasing throughput of the satellite system. Thelaser beams are received by a RX of an optical space terminal, whereinthe optical space terminal and the optical ground terminal are paired bythe satellite system configuration, such that receiving apertures of theoptical space terminal and transmitting apertures of the optical groundterminal are configured to aim to each other for the bi-directionalcommunication.

At step 850, the laser beams of one of the multiple forward channels areselected and received, and the received laser beams are amplified by anoptical power amplifier (PA) and/or an optical low-noise amplifier(LNA), and further are demodulated by a demodulator. The modulated andamplified optical signals are converted into interleaved codewords by anoptical modem.

At step 860, the interleaved codewords are deinterleaved by a channeldeinterleaver, and further are decoded by a physical layer FEC decoderinto pre-interleaved ordered codewords.

At step 870, the physical layer data frames may be regenerated intodata-link layer data packets, or any data packets at a layer higher thanphysical layer. The higher layer data packets can be transferred fromone optical space terminal to another optical space terminal on thespacecraft, wherein each of the optical space terminal may be associatedwith a particular destination (e.g., a corresponding optical groundterminal). Thus, the data packets are transmitted from one destinationto another destination.

FIG. 9 illustrates another example method of optical satellitecommunication in accordance with particular embodiments.

In particular embodiments, a return channel communication 900 may startat step 910, data-link layer data packets are received by a TX of anoptical space terminal, wherein the received data-link layer datapackets are encoded by a data-link layer packet erasure forward errorcorrection (FEC) encoder. The received data-link layer data packets arefirst arranged into a plurality of data frames, and the plurality ofdata frame are encoded by the data-link layer packet erasure FECencoder. The number of the data frames before encoding may be differentthan the number of the encoded data frames. The encoded data frames thenare sent to the physical layer.

At step 920, the encoded data frames are received from the data-linklayer. The received encoded data frames are processed at the physicallayer in a data channel. Within the data channel, the encoded dataframes are encoded again by a physical layer FEC encoder into codewords.Then the codewords are interleaved by a channel interleaver.

At step 930, the interleaved encoded data frames are inputs to anoptical modem which perform the conversion between the electricalsignals and optical signals. The outputs of the optical modem are theoptical signals, wherein the optical signals are modulated by amodulator. After being modulated, the optical signals are amplified byan optical power amplifier (PA) and/or an optical low-noise amplifier(LNA). The modulated and amplified optical signals are coupled withlaser beams by a beam control, wherein the beam control also ensure thatthe transmitting apertures of the optical ground terminal are aimed tothe receiving apertures of a respective optical ground terminal.

At step 940, the laser beams are transmitted through the air or vacuumvia a single return channels. The laser beams are received by acounterpart RX of an optical ground terminal, wherein the optical groundterminal and the optical ground terminal are paired by the satellitesystem configuration, such that receiving apertures of the opticalground terminal and transmitting apertures of the optical space terminalare configured to aim to each other for the bi-directionalcommunication.

At step 950, the laser beams are received and selected by one of thedata channels. In selected data channel, the received laser beams areamplified by an optical power amplifier (PA) and/or an optical low-noiseamplifier (LNA), and further are demodulated by a demodulator. Themodulated and amplified optical signals are converted into interleavedcodewords by an optical modem.

At step 960, the interleaved codewords are deinterleaved by a channeldeinterleaver, and further are decoded by a physical layer FEC decoderinto pre-interleaved ordered codewords.

At step 970, the physical layer data frames may be regenerated intodata-link layer data packets, or any data packets at a layer higher thanphysical layer. The higher layer data packets can be transferred to anetwork layer. Thus, a cycle of data transfer from one destination toanother destination is completed.

Herein, a computer-readable non-transitory storage medium or media mayinclude one or more semiconductor-based or other integrated circuits(ICs) (such, as for example, field-programmable gate arrays (FPGAs) orapplication-specific ICs (ASICs)), hard disk drives (HDDs), hybrid harddrives (HHDs), optical discs, optical disc drives (ODDs),magneto-optical discs, magneto-optical drives, floppy diskettes, floppydisk drives (FDDs), magnetic tapes, solid-state drives (SSDs),RAM-drives, SECURE DIGITAL cards or drives, any other suitablecomputer-readable non-transitory storage media, or any suitablecombination of two or more of these, where appropriate. Acomputer-readable non-transitory storage medium may be volatile,non-volatile, or a combination of volatile and non-volatile, whereappropriate.

Herein, “or” is inclusive and not exclusive, unless expressly indicatedotherwise or indicated otherwise by context. Therefore, herein, “A or B”means “A, B, or both,” unless expressly indicated otherwise or indicatedotherwise by context. Moreover, “and” is both joint and several, unlessexpressly indicated otherwise or indicated otherwise by context.Therefore, herein, “A and B” means “A and B, jointly or severally,”unless expressly indicated otherwise or indicated otherwise by context.

The scope of this disclosure encompasses all changes, substitutions,variations, alterations, and modifications to the example embodimentsdescribed or illustrated herein that a person having ordinary skill inthe art would comprehend. The scope of this disclosure is not limited tothe example embodiments described or illustrated herein. Moreover,although this disclosure describes and illustrates respectiveembodiments herein as including particular components, elements,feature, functions, operations, or steps, any of these embodiments mayinclude any combination or permutation of any of the components,elements, features, functions, operations, or steps described orillustrated anywhere herein that a person having ordinary skill in theart would comprehend. Furthermore, reference in the appended claims toan apparatus or system or a component of an apparatus or system beingadapted to, arranged to, capable of, configured to, enabled to, operableto, or operative to perform a particular function encompasses thatapparatus, system, component, whether or not it or that particularfunction is activated, turned on, or unlocked, as long as thatapparatus, system, or component is so adapted, arranged, capable,configured, enabled, operable, or operative. Additionally, although thisdisclosure describes or illustrates particular embodiments as providingparticular advantages, particular embodiments may provide none, some, orall of these advantages.

1. An apparatus comprising: one or more optical ground terminals,wherein each optical ground terminal comprises a forward channeltransmitter (TX) and a return channel receiver (RX), wherein eachoptical ground terminal is paired with a counterpart optical spaceterminal, and wherein the forward channel TX is configured to: receive aplurality of data frames at a data-link layer; encode the plurality ofreceived data frames by a data-link layer encoder, wherein the data-linklayer encoder is a packet erasure encoder using a forward errorcorrection (FEC) code; distribute the plurality of encoded data framesto a plurality of data channels by a distributor, wherein forwardchannel data is generated by the plurality of data channels with respectto the plurality of encoded data frames; encode the plurality of encodeddata frames into codewords by a physical layer encoder within each ofthe plurality of data channels, wherein the physical layer encoder is anFEC channel encoder; and embed the forward channel data to a pluralityof uplink beams by a plurality of optical modems in each of theplurality of data channels, respectively, wherein the plurality ofoptical modems convert the codewords to a plurality of optical signals,wherein the plurality of uplink beams is amplified by one or moreoptical power amplifiers (PA), and the plurality of uplink beams istransmitted via multiple forward channels through air/vacuum.
 2. Theapparatus of claim 1, wherein the plurality of uplink beams is receivedby a counterpart forward channel receiver (RX) in a respective opticalspace terminal.
 3. The apparatus of claim 1, wherein the forward channelTX comprises one or more optical low noise amplifiers (LNA) configuredto amplify the plurality of uplink beams, physical layer FEC encoders,channel interleavers, and modulators in the plurality of data channelsrespectively.
 4. The apparatus of claim 1, wherein the return channel RXis configured to: receive one or more downlink beams via a returnchannel through air/vacuum by one of the data channels, wherein the oneof the data channels is selected by a selector; extract return channeldata from the one or more downlink beams by an optical modem in the oneof the data channels, wherein the one or more downlink beams areamplified by an optical power amplifier (PA) in the one of the datachannels, and encoded data frames are generated by the one of the datachannels with respect to the return channel data; and at a data-linklayer, decode the encoded data frames by a data-link layer decoder,wherein the data-link layer decoder is a packet erasure decoder using aforward error correction (FEC) code.
 5. The apparatus of claim 4,wherein the one or more downlink beams are transmitted from acounterpart return channel transmitter (TX) in a respective opticalspace terminal.
 6. The apparatus of claim 4, wherein the return channelRX comprises a physical layer FEC decoder, a channel deinterleaver, anda demodulator.
 7. An apparatus comprising: one or more optical spaceterminals, wherein each optical space terminal comprises a returnchannel transmitter (TX) and a forward channel receiver (RX), whereineach optical space terminal is paired with a counterpart optical groundterminal, and wherein the return channel TX is configured to: receive aplurality of return data frames at a physical layer; encode theplurality of received return data frames into codewords by a physicallayer encoder, wherein the physical layer encoder is a forward errorcorrection (FEC) encoder; and embed the plurality of encoded return dataframes to one or more downlink beams by an optical modem in a datachannel, wherein the optical modem converts the codewords to one or moreoptical signals, wherein the one or more downlink beams are amplified byan optical power amplifier (PA), and the one or more downlink beams aretransmitted via a return channel through air/vacuum.
 8. The apparatus ofclaim 7, wherein the one or more downlink beams are received by acounterpart return channel receiver (RX) in a respective optical groundterminal, and the respective optical ground terminal is paired with oneof the optical space terminals for optical communication.
 9. Theapparatus of claim 7, wherein the return channel TX comprises a channelinterleaver, a modulator, and an optical low noise amplifier (LNA)configured to amplify the one or more downlink beams.
 10. The apparatusof claim 7, wherein the forward channel RX is configured to: receive oneor more uplink beams via one of multiple forward channels throughair/vacuum; extract forward channel data from the one or more uplinkbeams by an optical modem in a data channel, wherein the one or moreuplink beams are amplified by an optical power amplifier (PA) in thedata channel; and decode the forward channel data into decoded dataframes by a physical layer decoder, wherein the physical layer decoderis a forward error correction (FEC) decoder.
 11. The apparatus of claim10, wherein the one or more uplink beams are transmitted from acounterpart forward channel transmitter (TX) in a respective opticalground terminal.
 12. The apparatus of claim 10, wherein the forwardchannel RX comprises a plurality of physical layer FEC decoders, channeldeinterleavers, and demodulators.
 13. A system comprising: one or moreoptical ground terminals, and a spacecraft having at least one or moreoptical space terminals and a space switch unit, wherein the spacecraftis configured to: receive a plurality of encoded data frames by aforward channel RX of one optical space terminal from a counterpartforward channel TX of a respective optical ground terminal at a datarate of 1 terabits-per-second (Tbps) or above via multiple forwardchannels through air/vacuum, wherein the respective optical groundterminal is paired with the optical space terminal for datacommunication, and the encoded data frames are encoded by thecounterpart forward channel TX of the respective optical groundterminal; decode the plurality of encoded data frames by the forwardchannel RX of the optical space terminal; regenerate a plurality of datapackets based on the plurality of decoded data frames by the spaceswitch unit, wherein the data packets are at a layer of data-link orhigher; and route the regenerated data packets to another optical spaceterminal by the space switch unit, wherein another optical spaceterminal is paired with another optical ground terminals for datacommunication.
 14. The system of claim 13, wherein the space switch unitcomprises at least a space switch and a RF channel former, wherein theRF channel former has a regenerative multi-channel RF modem.
 15. Thesystem of claim 14, wherein the regenerative multi-channel RF modem hasa power amplifier (PA) and/or a low noise amplifier (LNA) in eachchannel.
 16. The system of claim 14, wherein the space switch is aterabit switch conducting data packet switch at the layer of data-linkor higher.
 17. The system of claim 14, wherein the space switch is amake-before-break (MBB) switch detecting upcoming communicationinterruption and redirecting ongoing data communication from one of theoptical space terminals to another one of the optical space terminals.18. The system of claim 13, wherein the spacecraft is further configuredto: transmit a plurality of encoded data frames by a return channel TXof one of optical space terminals to a counterpart return channel RX ofa respective optical ground terminal at a data rate of 1terabits-per-second (Tbps) or above via a return channel throughair/vacuum, wherein the optical space terminal is paired with therespective optical ground terminals for data communication, and theencoded data frames are encoded by the return channel TX of the opticalspace terminal; decode the plurality of encoded data frames by thecounterpart return channel RX of the respective optical ground terminal;and regenerate a plurality of data packets based on the plurality ofdecoded data frames by the counterpart return channel RX of therespective optical ground terminal, wherein the data packets are at alayer of data-link or higher.
 19. The system of claim 18, wherein thespacecraft is further configured to transmit the plurality of datapackets to a network layer.
 20. The apparatus of claim 1, wherein theforward channel TX comprises an optical beam control configured todirect transmitted uplink beams to a counterpart forward channelreceiver (RX) in the respective counterpart optical space terminal.